1. Field of the Invention
The present invention relates to an actuator device with a valve for use in a device for controlling a flow rate of a fluid in a pipe wherein a toroidal core type actuator is used to directly open or close a valve based on an angle command value and, more particularly, to an actuator device with an engine throttle valve to be mounted on a vehicle.
2. Description of Related Art
Recently, a drive by wire system is widely used to improve automobile drivability and to accomplish counter-measures for exhaust gas. The drive by wire system, which does not use an accelerator cable, electrically detects by a sensor a depression amount of an accelerator pedal stepped by a driver and drives an engine throttle valve by a motor, thus operating the engine throttle valve completely independently of the operation of the accelerator pedal performed by the driver. As a result, the drive by wire system makes it possible to control engine output while always securing an appropriate air-fuel ratio for each situation, and therefore has been attracting attention and spreading as one of solutions to environmental problems.
In currently available drive by wire systems, however, throttle valves are usually driven by a combination of DC motors and decelerators as described in Japanese Laid-open Patent Application No. 5-240070 and U.S. Pat. No. 5,777,412. This is because driving a throttle valve requires a large torque ranging from about 30 to about 60 Ncm (230 Ncm in a freeze condition), so that the required torque cannot be provided by a motor alone unless torque is increased by the intermediary of a decelerator. Using the decelerator, however, adds to cost of a system and deteriorates reliability. Above all, the conventional drive by wire systems have a shortcoming in that highly accurate flow rate control cannot be achieved due to backlash of gears or the like.
There has been also known a direct drive system that uses a toroidal core type actuator having a rotary shaft that repetitively rotates. If an operating angle range of the rotary shaft is limited to about 0 degree to about 90 degrees, then the torque characteristic depends solely on an input current value and not depends on the angle. This characteristic is ideally suited for controlling rotational angles (the details will be described hereinafter). Making use of this characteristic, it is possible to control a flow rate with high accuracy by providing a pipe through which a fluid passes with a shaft orthogonalized with respect to an axis of the pipe, attaching a butterfly valve to the shaft, and by controlling the angle of the valve. This technology has been applied to a variety of attempts to directly drive an engine throttle valve. However, required torque is large for a size (e.g. a diameter of about 70 mm and a length of about 70 mm). Thus, no actuators that are adequate for practical use have been available.
However, high-performance magnet made of a rare earth element has been developed, leading to prospects of accomplishing rotor magnets in appropriate sizes that are capable of producing the required torque of about 30 to about 60 Ncm for driving throttle valves. Stators have been presenting shortcomings in that workability of toroidal winding process itself is poor, handling after the winding process is difficult, and accomplishing dimensional accuracy is difficult, either. Therefore, the stators have been disadvantageous in that it is difficult to install onto apparatuses with high accuracy, which has been a cause of higher cost.